Donny and Marie are pros at this

The Osmond siblings might well be the precursors to 'American Idol' and Taylor Swift. The do-it-all duo are in residence this holiday in Hollywood.

Donny and Marie Osmond are performing a holiday show in Los Angeles. (Mark Boster, Los Angeles…)

Donny and Marie Osmond hit the stage at the Pantages Theatre in a cloud of nearly palpable pizazz.

For two hours the indefatigable showbiz veterans, kicking off "A Donny and Marie Christmas in Los Angeles," sang, danced and smiled — oh, did they smile — with a weapons-grade enthusiasm that belied their seen-it-all experience.

At one point on opening night Tuesday, a visibly sweat-streaked Donny, 54, blazed through a rat-a-tat mash-up of the Rolling Stones' "Start Me Up," "Dynamite" by Taio Cruz and, just for good measure, a line or two from the Korean pop smash "Gangnam Style."

The people in the crowd — many there as fans, some no doubt digging for kitsch — cheered the siblings with equivalent force.

If Donny & Marie came to fame preaching the gospel of musical diversity — think "I'm a Little Bit Country, I'm a Little Bit Rock and Roll" — their belief in that approach is equally firm today. Even their so-called Christmas show ventures well beyond sleigh bells and mistletoe.

"We decided it couldn't be wall-to-wall Christmas music," an exceptionally trim and dapper Donny had explained earlier. "You'd have to leave with an insulin shot."

That mix-and-match sensibility — and a deeply committed professionalism, no matter how iffy the material — help explain why Donny & Marie can still attract an audience a half-century into their respective careers.

"Christmas in Los Angeles" runs through Dec. 23, and robust ticket sales are testament to a wholesome allure that's faded little since Nixon was in office.

The duo's cover-every-corner approach — albums, a weekly TV show, "Dancing With the Stars," even Marie's deal with Nutrisystem — almost makes you wonder if the Osmonds were ahead of their time. Or at least if the rest of the entertainment world has finally caught up with them.

Genre-hopping singing shows such as "American Idol" and "The Voice," as well as Nickelodeon-made pop stars, all recall the days when this shiny, happy twosome ruled late-'70s variety TV.

"Thank you for the compliment," Donny said with a grin when presented with the possibility that he and his sister were ahead of the curve. "They're not just doing pop songs [on those shows] — they're doing all kinds of stuff," he went on. "So, really, it's variety again. It's giving you the whole pie instead of just one piece."

"It's not easy to do all these styles: country, rock, jazz, Broadway, opera," said Marie, who with Donny brought an earlier version of the Christmas show to Broadway in 2010. "But we've both spent a lot of time working on it. And that's what defines longevity, if you can do it all. I think entertainers see that nowadays."

Yet with the clock ticking ever forward, the stars' handlers began glancing at their watches: Donny & Marie were due onstage at 7:30 that evening — and not at the Pantages, but in Las Vegas, where they've been playing the Flamingo Showroom on a near-nightly basis since 2008.

"You want to know something even crazier?" Donny asked, leaning into a reporter more closely than might've been expected. "Last week we were in London."

"For one day!" Marie added, leaning a bit herself.

"We flew out Saturday night after the show," Donny continued, "then came back Tuesday morning and did a show that night."

How does one learn to survive such a go-go regimen?

"Well, it's what we've been doing all our lives," Donny replied. "She started when she was 3; I was 5. You grow up in that lifestyle, that's what normalcy is."

"You adapt," Marie said. "You learn to bring it when you have to."

The Osmonds said they learned that lesson early on, as the most visible members of a Utah-based family operation that became the white Mormon answer to the Jacksons.

They took their cues from the greats they grew up observing — Elvis Presley, Frank Sinatra, Sammy Davis Jr. — and recognize it now in the likes of Kelly Clarkson and Taylor Swift, singers who "give the audience a piece of themselves," as Donny described them.

"Remember Taylor with the banjo on the [2012] Grammys?" he asked. "She came out and sang her song ['Mean'], and her personality came across. And what happened? Standing ovation."